In a display used for a personal computer and others, the rewriting of the screen, that is, the so-called refresh is performed about several tens of times per second so as to prevent the flicker of the screen.
As the frequency of this refresh, that is, the so-called refresh rate becomes higher, the flicker is reduced more. The refresh rate is set to, for example, a constant value of about 50 Hz to about 70 Hz.
The performance of the display has a close relation with the performance of the image processor mounted on the personal computer, that is, the GPU (Graphics Processing Unit) and others. For example, since the drawing speed is slow in the case of a GPU with a slow operating speed, there is a fear that the next frame is not drawn within the refresh period and the same frame is displayed. Thus, there is a problem that the display performance of the display is lowered.
As the techniques for solving this problem, there are those that vary the refresh rate (for example, see Patent Document 1 and Patent Document 2). Patent Document 1 describes that, based on the drawing processing time of an image being output by a video source device and the output time of one screen calculated from a refresh rate value, the refresh rate value is modified.
In addition, Patent Document 2 describes a refresh rate variation technique in which, when a video source device draws one frame, the video source device outputs a video signal and the display panel displays the one frame, and if the drawing time exceeds a predetermined time and the display signal is not output, the display panel displays a previous frame.